This application relates generally to microelectromechanical systems (“MEMS”). More specifically, this application relates to methods and systems for protecting interconnect structures in MEMS.
There are various known techniques for providing protective structures in the field of integrated circuits. For example, it is common to form an integrated-circuit structure through the deposition of various layers of materials and to complete the process by depositing a passivation layer over the resulting layered structure. Furthermore, the integrated circuits may also be capped with a plastic material to prevent their destruction. In the case of MEMS, protection of components is complicated by the existence of active mechanical components, which in some instances need to be exposed to the atmosphere for the device to operate as desired. In these applications, a passivation layer cannot be applied to the entire structure because it would interfere with the movement of the active mechanical components.
Thus, in MEMS packaging, conductors may sometimes be exposed to the atmosphere, permitting contamination by particulate matter that may interfere with the operation of the device. For example, a typical MEMS device includes a plurality of interconnect traces, with each trace being designed to connect to a single element of the device. The presence of contaminant debris between two (or more) traces may tie those traces together electrically so that they no longer connect to a single element. Even worse, the location of contaminant debris may electrically tie the trace to ground, resulting in a true electrical short circuit than renders the entire MEMS device nonfunctional. In some instances, the electrical short circuit may result in arcing, melting, or welding, causing destruction of the device.
Contaminant particles may arise from different sources. For example, they may occur as dirt particles that exist in the atmosphere in which the device is manufactured. Filtering techniques are used to limit the presence of dirt particles, but these techniques are imperfect. More typically, the manufacturing process itself results in fragments of silicon that are not completely removed during fabrication steps. This may occur, for example, during the removal of sacrificial material, resulting in contaminant “stringers.” Also, handling of the devices may induce chipping or fracturing at the edges of the material.
There is, therefore, a general need in the art for methods and systems to mitigate the damage caused to MEMS devices resulting from electrical interference by contaminant particles.